One or more ultrasonic sensors may be mounted on an automotive vehicle, for example a hybrid electric vehicle (HEV), enabling a distance determination between the sensor and an external object. Such an ultrasonic sensor may consist of at least a piezoelectric disc and a membrane, configured to convert electrical energy into mechanical energy, and mechanical energy into electrical energy. More specifically, an oscillated voltage may be applied to the piezo disc such that the piezo disc and membrane vibrate and generate ultrasonic waves at a frequency based on the frequency of voltage oscillation. After the waves are emitted, sensors wait for echoes to come back from objects, and when the echoes interact with the sensor/membrane, the membrane is excited to vibrate. The piezo disc attached to the membrane converts the vibration to voltage, and based on the timeframe of sending and receiving the ultrasonic wave, a distance determination to an object may be inferred.
In a vehicle, ultrasonic sensors may be utilized for inferring distance between a vehicle and obstacles during either assisted, or fully automated parking, for example. However, a number of factors may play a role in the operational use of ultrasonic sensors. Such factors may include temperature, humidity, target surface angle, and reflective surface roughness. Of these four variables, determining humidity in a vehicle may be complicated, particularly in a case where a vehicle may not include a dedicated humidity sensor. Furthermore, estimation of ambient humidity may be important for a number of engine operating parameters, such as an amount of exhaust gas recirculation (EGR), spark timing, combustion air-fuel ratio, etc. Thus, knowledge of ambient humidity may improve operational use of ultrasonic sensors, and may be further utilized to adjust relevant engine operating parameters.
Various kinds of sensors may be used to estimate the ambient humidity. As one example, oxygen sensors, such as a Universal Exhaust Gas Oxygen (UEGO) sensor used for exhaust air-fuel ratio control, may be used for ambient humidity estimation under selected conditions. Such oxygen sensors can be located in an exhaust passage or an intake air passage. In one example, shown by Surnilla et al. in US 20140202426, an exhaust gas oxygen sensor coupled to an engine bank may be utilized to opportunistically determine ambient humidity during conditions when the bank is selectively deactivated, and while the other bank continues to combust. A variable voltage may be applied to the sensor, and a change in pumping current may be correlated with the ambient humidity.
However, the inventors herein have recognized potential issues with such a system. As one example, humidity measurements may be non-specific, where humidity is estimated either opportunistically when possible, or when desired. Still further, where an exhaust oxygen sensor is used for humidity sensing, frequent application of a variable voltage may result in sensor blackening, and eventual degradation.
In another approach, US Patent Application US 20060196272 teaches the use of an ultrasonic sensor configured to transmit two different frequencies, and estimate humidity based on a difference between attenuation losses obtained from the two different frequencies. However, the inventors herein have recognized potential issues with such systems. As one example, there may be certain times where determination of humidity via ultrasonic sensors may be compromised due to environmental or other variables. In another example, in cases where the ultrasonic sensor or other ultrasonic sensor may additionally be configured to determine distance measurements, it may be desirable to indicate suitable frequencies for conducting the distance measurements, where the suitable frequencies may be based on the humidity determination.
Thus, the inventors herein have developed systems and methods to at least partially address the above issues. In one example, a method is provided, comprising transmitting a plurality of signals from a single sensor, each at a different frequency; receiving reflected signals of the transmitted signals; changing frequency of the transmitted signals to achieve a desired signal-to-noise; determining attenuation values only for each of the reflected signals which have the same transit time from transmission to receipt; determining differences between pairs of the attenuation values; and converting the differences to an indication of relative humidity.
As one example, the frequencies of the transmitted signals are changed in response to a determination that the reflected signals have or would have any undesired signal-to-noise ratio. As another example, the frequency of the transmitted signals are changed in response to environmental conditions including one or more of the following: ambient temperature, ambient humidity, and the transit time from transmission to receipt of the transmitted and the reflected signals.
Another example further comprises adjusting a distance detection threshold with the indicated relative humidity, where adjusting the distance detection threshold includes indicating suitable frequencies for conducting a distance measurement; and selecting an optimal frequency to conduct the distance measurements responsive to the adjusted distance detection threshold. As an example, the method further comprises equipping a motor vehicle with the sensor and detecting an absence of a parked vehicle to assist in parallel parking of the motor vehicle by selecting a frequency or frequencies corresponding to the adjusted distance detection threshold.
In this way, an ultrasonic sensor may be utilized to determine relative humidity. By changing frequencies responsive to indications that the received signals have or may have undesired signal-to-noise ratios, or responsive to environmental conditions, accurate humidity measurements may be obtained by the ultrasonic sensor. Furthermore, by adjusting a distance detection threshold, optimal frequency(s) may be selected for distance measurements, such as distance measurements conducted during assisted or fully automated parking maneuvers, for example.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.